I recently bought one of those 1.5MCP aluminum vector spotlights...as you know it's about as bright as an arc welder, and only lasts about 25 minutes on a charge. Is there a relatively easy way to add an adjustable dimmer to the light? Something that would make the battery last longer...would adding resistors do that? Or do they just eat up the extra voltage?
How can I dim a light?
- Thread starter zmoz
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Rothrandir
Flashaholic
you could try a pot dimmer...
then you will have adjustable output /ubbthreads/images/graemlins/grin.gif
just be sure you get one beefy enough to handle whatever current you're going to give it.
then you will have adjustable output /ubbthreads/images/graemlins/grin.gif
just be sure you get one beefy enough to handle whatever current you're going to give it.
Wim Hertog
Enlightened
Resistors or a pot dimmer won't work...they'd have to handle 50 or 100 watts!! The only thing you could do is design a smal variable voltage source with a small pot and 2 power transistors /ubbthreads/images/graemlins/smile.gif
You have a traditional problem, made extreme by the levels involved. In broad terms, consider cutting current in half. Ignoring the funny resistance vrs temperature thing with bulbs (not trivial), considering them straight resistance, this means half the voltage drop. The battery stays the same voltage, meaning that the difference, half the total battery voltage (same as lamp voltage in this case) is 'across the series resistor'. As another poster has hinted, this means not only is half the power we're taking from the battery wasted in heat, but the resistor in question must be robust indeed. Ironically, often lamps are used in similar cases since they can get rid of a lot of energy as light rather than heat directly. True, the total battery current is half the stock case, but in terms of watts, we've wasted half.
However, lamps work by heat. If we turn it on and off ('full blast' when on, zero when off) fairy quickly, it all 'blends together' as heat. This is how household light dimmers work. Even though they control hundreds of watts, they stay cool since they are nearly perfect, high speed, 'switches'. Always either full on or full off, just changing rapidly. The lamp filament, because of it's thermal mass, responds to the 'average current'.
As you might guess, such circuits are challenging. If it hangs up you have problems. Either too bright, not lit or burnt up (Murphy enters favoring the latter historically). There can also be thermal issues in the controller. While higher temps favor us usually (gains go up for instance) sometimes it works against us (leakages go up as well). Thermal run away is a common fault mode.
Then there's the whole issue of poor lamp performance at lower drive levels.
If you want less light either buy a lower powered unit, or use a lower power bulb in the one you have. If you want the 'quick and dirty' solution to variable power, try some hunky diodes in series. High power diodes are often cheaper and easier to find. It's also possible to make a switch selectable power setup with a string of them (you get .7 or so less volts per). If your current is under 6 Amps, Jameco has some attractive ones in the 'easy to deal with' T6L case (no heatsink needed) at 29 cents each. Check out their part number 177762. As an added bonus to such a system, you can switch diodes out to maintain light output as the battery discharges.
Or so I see it.
Doug Owen
However, lamps work by heat. If we turn it on and off ('full blast' when on, zero when off) fairy quickly, it all 'blends together' as heat. This is how household light dimmers work. Even though they control hundreds of watts, they stay cool since they are nearly perfect, high speed, 'switches'. Always either full on or full off, just changing rapidly. The lamp filament, because of it's thermal mass, responds to the 'average current'.
As you might guess, such circuits are challenging. If it hangs up you have problems. Either too bright, not lit or burnt up (Murphy enters favoring the latter historically). There can also be thermal issues in the controller. While higher temps favor us usually (gains go up for instance) sometimes it works against us (leakages go up as well). Thermal run away is a common fault mode.
Then there's the whole issue of poor lamp performance at lower drive levels.
If you want less light either buy a lower powered unit, or use a lower power bulb in the one you have. If you want the 'quick and dirty' solution to variable power, try some hunky diodes in series. High power diodes are often cheaper and easier to find. It's also possible to make a switch selectable power setup with a string of them (you get .7 or so less volts per). If your current is under 6 Amps, Jameco has some attractive ones in the 'easy to deal with' T6L case (no heatsink needed) at 29 cents each. Check out their part number 177762. As an added bonus to such a system, you can switch diodes out to maintain light output as the battery discharges.
Or so I see it.
Doug Owen
Rothrandir
Flashaholic
how about a wall dimmer...like the kind you dim your ceiling lights with?
would that work?
would that work?
Tomas
Banned
[ QUOTE ]
Rothrandir said:
how about a wall dimmer...like the kind you dim your ceiling lights with?
would that work?
[/ QUOTE ]
Only if he has one of my old electronics instructor's "AC Batteries" on hand. /ubbthreads/images/graemlins/grin.gif
(Aside: Waaay back when I was taking one of my early electronics courses (1963), my instructor would always draw a battery as the power source regardless if the source was AC or DC.
It was just simpler to show a battery and mark it "AC" than it was to get really complicated and off topic by showing some sort of power supply. We did ask why he didn't just show a "black box" AC source, and his reply was that it was simpler and quicker to use the easy to recognize "battery" at this stage of our learning.
Of course we couldn't just let that lie, eh?
We very carefully took apart one of those big, hulking rectangular lantern batteries and replaced one of the half-that-size 6V square lantern batteries inside with a DC to AC converter - I think it used a couple of 2N256's, etc. It was set up to NOT draw power unless there were a load attached.
We put the battery case back together and gave it a really nice paint job. It was now a "Ken Kegley AC Battery." We gave it to Ken, our instructor, at the end of that semester.
He loved that thing, and had it "fixed" several times when it died.
He would just WAIT for someone to challenge his "AC Battery" in a schematic so he could whip that thing out and show them his genuine, one-off, AC Battery.)
Rothrandir said:
how about a wall dimmer...like the kind you dim your ceiling lights with?
would that work?
[/ QUOTE ]
Only if he has one of my old electronics instructor's "AC Batteries" on hand. /ubbthreads/images/graemlins/grin.gif
(Aside: Waaay back when I was taking one of my early electronics courses (1963), my instructor would always draw a battery as the power source regardless if the source was AC or DC.
It was just simpler to show a battery and mark it "AC" than it was to get really complicated and off topic by showing some sort of power supply. We did ask why he didn't just show a "black box" AC source, and his reply was that it was simpler and quicker to use the easy to recognize "battery" at this stage of our learning.
Of course we couldn't just let that lie, eh?
We very carefully took apart one of those big, hulking rectangular lantern batteries and replaced one of the half-that-size 6V square lantern batteries inside with a DC to AC converter - I think it used a couple of 2N256's, etc. It was set up to NOT draw power unless there were a load attached.
We put the battery case back together and gave it a really nice paint job. It was now a "Ken Kegley AC Battery." We gave it to Ken, our instructor, at the end of that semester.
He loved that thing, and had it "fixed" several times when it died.
He would just WAIT for someone to challenge his "AC Battery" in a schematic so he could whip that thing out and show them his genuine, one-off, AC Battery.)
Rothrandir
Flashaholic
hmmm a wall dimmer can't do dc?
didn't know that...
didn't know that...
brightnorm
Flashaholic
- Joined
- Oct 13, 2001
- Messages
- 7,160
Tom,
that was a very nice thing to do, the class must really have liked him
(sorry, off topic)
Brightnorm
that was a very nice thing to do, the class must really have liked him
(sorry, off topic)
Brightnorm
Icebreak
Flashlight Enthusiast
brightnorm -
This is one of those very rare times that I might disagree with you. I think your post was more on topic than most posts I read. It had to do with the comradery that takes place within skilled groups of individuals that have mutual respect for one another resulting in kindness and consideration. Sure, I'll bet Tomas' crew razzed that instructor occasionally but only after they were all clear that he knew he was tops in thier view.
It is this type of thing that causes me to come to CPF so often during the week. I think the main topic at CPF is comradery.
zmoz -
I apologize for my OT to address an OT.
BTTT: How can I dim a light?
Let someone borrow it.
OK. I'll pay for that one. /ubbthreads/images/graemlins/ohgeez.gif /ubbthreads/images/graemlins/grin.gif
This is one of those very rare times that I might disagree with you. I think your post was more on topic than most posts I read. It had to do with the comradery that takes place within skilled groups of individuals that have mutual respect for one another resulting in kindness and consideration. Sure, I'll bet Tomas' crew razzed that instructor occasionally but only after they were all clear that he knew he was tops in thier view.
It is this type of thing that causes me to come to CPF so often during the week. I think the main topic at CPF is comradery.
zmoz -
I apologize for my OT to address an OT.
BTTT: How can I dim a light?
Let someone borrow it.
OK. I'll pay for that one. /ubbthreads/images/graemlins/ohgeez.gif /ubbthreads/images/graemlins/grin.gif
Use Pulse Width Modulation, you will get greater efficiencies this way than you would with simple series regulators.
a simple search for 'pulse width modulation' will give you some circuits e.g.
http://www.aaroncake.net/circuits/motorcon.htm
a simple search for 'pulse width modulation' will give you some circuits e.g.
http://www.aaroncake.net/circuits/motorcon.htm
Sorry tonyb,
I was not trying to jump in on your post, but with sugestions like using a 'pot' or 'dimmer switch' were so far off the mark I felt I had to not only re-inforce your comments, but also give a simple explanation of the benefits of PWM.
p.s. I have used PWM on many occasions, ususally I make a two transistor multivibrator but replage two of the resistors with a single pot. This will give you the full sweep from zero power to 100% power(less the power dissipation across the transistor), whereas when usin a 555 timer you go not go fully to these extremes.
e.g. take the following circuit:
http://www.4qdtec.com/mvbz/mv1a.gif
from the webpage at:
http://www.4qdtec.com/mvibs.html
remove r1 and r3 and connect the two ends of a pot where they are connected to the capacitors. connect a resistor (equal in value to r2 or r4) from the wiper of the pot to vcc, this base current limiting resistor will prevent you from killing your pot at when you move to the end of the stroke. Use a connection at the collector of one of transistors to drive the output stage, typically a high gain (Darlington), high frequency transistor. i.e. connect the output transistor base to one of the oscilator transistors, connect the output transistoe emitter to 0v, and connect the load between +v and the output transistor collector.
If you stick with the values shown (the original circuit is stated to run at about 1khz) then a 1 meg pot will mean yor circuit will 'chop' at just under 1khz so your power transistor will need to be ok for switching this frequency.
note: if you wish to switch inductive loads e.g. motors remember to add a flywheel diode to the output stage (connected the wrong way round so no current will flow through it when circuit is switched on), also not that 1khz is in the audible range, so the motor will sound like an electric milk float (whines as it accelerates), so you will need to take the circuit frequency up above the human audible range (over 20 khz).
p.s. for any purists out there:
you can also add two trimmer pots, one each end of the 'adjuster' pot before you connect them to the capacitors, this will allow you to scale the positioning of the pot so you will have 0% to 100 % per sweep of the adjuster pot, or 20% to 90%, or 30% to 100% etc. whatever you wish it to be.
This circuit is regulary used by engineers when making electric model locomotives (not the hornby toys, the ones you can sit on and ride) powered by car batteries, and I have seen examples where the switching capacity exceeds 100 Amps.
I was not trying to jump in on your post, but with sugestions like using a 'pot' or 'dimmer switch' were so far off the mark I felt I had to not only re-inforce your comments, but also give a simple explanation of the benefits of PWM.
p.s. I have used PWM on many occasions, ususally I make a two transistor multivibrator but replage two of the resistors with a single pot. This will give you the full sweep from zero power to 100% power(less the power dissipation across the transistor), whereas when usin a 555 timer you go not go fully to these extremes.
e.g. take the following circuit:
http://www.4qdtec.com/mvbz/mv1a.gif
from the webpage at:
http://www.4qdtec.com/mvibs.html
remove r1 and r3 and connect the two ends of a pot where they are connected to the capacitors. connect a resistor (equal in value to r2 or r4) from the wiper of the pot to vcc, this base current limiting resistor will prevent you from killing your pot at when you move to the end of the stroke. Use a connection at the collector of one of transistors to drive the output stage, typically a high gain (Darlington), high frequency transistor. i.e. connect the output transistor base to one of the oscilator transistors, connect the output transistoe emitter to 0v, and connect the load between +v and the output transistor collector.
If you stick with the values shown (the original circuit is stated to run at about 1khz) then a 1 meg pot will mean yor circuit will 'chop' at just under 1khz so your power transistor will need to be ok for switching this frequency.
note: if you wish to switch inductive loads e.g. motors remember to add a flywheel diode to the output stage (connected the wrong way round so no current will flow through it when circuit is switched on), also not that 1khz is in the audible range, so the motor will sound like an electric milk float (whines as it accelerates), so you will need to take the circuit frequency up above the human audible range (over 20 khz).
p.s. for any purists out there:
you can also add two trimmer pots, one each end of the 'adjuster' pot before you connect them to the capacitors, this will allow you to scale the positioning of the pot so you will have 0% to 100 % per sweep of the adjuster pot, or 20% to 90%, or 30% to 100% etc. whatever you wish it to be.
This circuit is regulary used by engineers when making electric model locomotives (not the hornby toys, the ones you can sit on and ride) powered by car batteries, and I have seen examples where the switching capacity exceeds 100 Amps.
Here is a circuit maybe you can use it. I haven't tested it but it looks like it should work. Let me know if you need help crossing any of the components to Radio-Shack parts or others. U1 is a multivibrator, Q1 needs a small heatsink or maybe not. Sorry the picture is so big! Maybe if I have some time I will wire one up for testing. Thanks to our good friends at MOTOROLA. This might work for LEDS too.
I found an error, pin 3 at the top of U1 (555 timer) connect to the cathode of the 1N4004 should really be pin 8 or Vcc.
2.6 means pin 2 tied to pin 6 of U1.
I found an error, pin 3 at the top of U1 (555 timer) connect to the cathode of the 1N4004 should really be pin 8 or Vcc.
2.6 means pin 2 tied to pin 6 of U1.
I don't think you can dim that spotlight terribly usefully. Anything that lowers the power going into the filament will also lower the temperature, which will redden the color, pretty soon giving off mostly infrared. The same thing happens when you dim an AC-powered incandescent lamp. Once you dim it below 50% or so, you're getting red-orange light. Dimming seems to work a lot better with LED's, which don't change color with diminished power. The best way to control brightness in an incandescent is to have separate filaments for high and low power, like some Surefire flashlights have.
